Process for preparing metaldehyde



Patented Sept. 2, 1947 PROCESS FOR PBEPARIN G METALDEHYDE Richard S.Wilder, Elkins Park. Pm, aaslgnor to Publicier Industries Inc.Philadelphia, Pa.

No Drawing. Application November 2, 1944, Serial No. 561.643

9 Claims. 1

The present invention relates to the production of metaldehyde and itrelates more particularly to a process for producing metaldehyde inrelatively high yields by polymerizing acetaldehyde.

An object of the present invention is to provide a new and improvedprocess for producing metaidehyde by polymerization of acetaldehyde.Another object of the present invention is to provide a process forpolymerizing acetaldehyde to give high yields of metaldehyde whileminimizing the production, and preventing the precipitation, ofparaldehyde.

Other objects and advantages of the present invention are apparent inthe following detailed description and appended claims.

Metaldehyde iCHzCI-IOl 4 has been known since 1835 (Ann. 14. 141). It isprepared by treating acetaldehyde at low temperatures with small amountsof acidic substances which catalyze polymerization. However, paraldehyde(CHsCHOh is ordinarily simultaneously formed in. much larger quantitiesand. indeed, unless the proper catalyst is employed and the temperaturecarefully controlled. the latter polymer is virtually the only productformed: the amount of metaldehyde formed being so small that little ornone of it crystallizes out. Various special catalysts have beensuggested in the past which favor the formation of metaldehyde, makingpossible metaldehyde yields of from our to eight per cent; as shown forexample in the following United States patents: Lilscher et al.1,467,733, Llischer et a1. 1,555,223. Lichtenhahn et al. 1,612,032.Liischer et al. 1,693,204 and Liischer et a1. 1,804,357. In all cases,the best yields are obtained when the polymerization is conducted attemperatures below -15C.

Since the principal product, paraldehyde, has a melting point of 10 0.,the reaction mixture becomes almost completely solid beforepolymerlzatlon is complete. This solidification of the reaction mixturemakes difllcult the recovery of metaldehyde therefrom since itnecessitates warming of the reaction mixture above 10 C. in order tomelt the paraldehyde before filtering oi! the desired product.Furthermore. the resulting delay and the rise in temperature adverselyail'ect the yield of metaldehyde.

I have now found that, by carrying out the polymerization of theacetaldchyde in the presence 01' an ether, I obtain much better results,in that Precipitation of the paraidehycle is prevented at temperaturesas low as C. and furthermore, considerably higher yields of metaldehydeare obtained than have ever been previously obtainable by the processesor the prior art.

Diethyl ether has been found to be particularly suitable in improvingthe yield of metaldehyde and in preventing precipitation of paraldehyde.Generally speaking. however. other allphatic ethers have been foundsatisfactory including, for example, methyl ethyl ether, diisopropylether. di-n-propyl ether, di-butyl ether, di-isobutyl ether, di-methyland dl-ethyl ethers of ethylene glycol, cyclic ethers such as dioxane,etc.

I prefer to employ for this purpose aliphatic ethers containing not morethan eight carbon atoms.

It is necessary to use only sumcient ether to prevent precipitation 01'the paraldehyde: approximately 7 to 15 per cent or the weight of theacetaldehyde being adequate in most cases.

While the ether prevents precipitation of the paraldehyde. it does notailect the precipitation 01' the metaldehyde and. accordingly, thelatter can be recovered by filtration.

After the metaldehyde has thus been removed. the ether and acetaldehydecan be recovered by distilling the filtrate in the presence of a smallamount of acid. which depolymerizes the paraldehyde.

If. however. it is desired to recover the paraldehyde as well, thefiltrate can be neutralized, by adding a little sodium carbonate orother suitable alkaline agent, and then distilled, whereby ether isrecovered from the distillate and paraldehyde is obtained in good yieldas a higher fraction.

The following are illustrative, but not restrictive, examples of theprocess of my present invention:

Example I Approximately seven parts (by weight) of diethyl ether ismixed with approximately parts of acetaldehyde and the mixture is cooledto approximately -20 C. A catalyst, compris ing approximately 0.48 partof 35% hydrobromic acid and approximately 0.15 part of pyridine. is thenadded with thorough stirring and cooling: the catalyst being added atsuch a rate that the temperature of the exothermic reaction mixture doesnot rise above approximately 0 C. The metaldehyde begins to crystallizeout while the catalyst is still being added. No precipitation whateverof paraldehyde occurs. The mixture is agitated for approximately onehour at approximately -5 to 0 C. and is then filtered. After removingthe filtrate from the receiver. the white. crystalline metaldehyde iswashed with obtained The procedure of Example 1 was repeated usingdi-n-propyl ether in piece oi the di-ethyl other with comparably goodresults.

Example 5Amixtureotepproximatelyiiiiipartsoiaceteldehzdeandapprouimatelympsrhoidiozaneiscooiedtoapproximately-Wilandtothe cooled mixture is added 0.45pm'totprridinehyph shydrohromio acid catalyst, containin: a 0.15 percent iree EBr; the catalyst being added cautiously with thorcushasitation and cooling sothatthetemperatureoithereactlonmimre does notrise above approximately 10' O. Thereaftenthemixtureisssitatedatapproxbmetal: 10' toil tor telyonehour andisthenflltered.Precipitationoltheparsldchydeispreventedend metaldelmisintheiormoisuhstsntiallypmewhitecrystalshohtaiaed inayieldampercenthisherthanthatresultinzwhenthedionaheisomitted.

Either acetaldehs'de or recoverediromtheiiltratesccordins canbe 00mm- 75pendedclslmsraflaerthantotheioresolnsdescriptiontoindicstethescopeoitheinventiou.7

Having thus described my invention, what Iclalmasnewanddesh'etoprotecthylettersi'atprises polymerisino proximately'0. inthepresenceotanalilihatic 2. A process for preparing meteldehydewhich comprises acetsldehyde below approximatelyIS'Qinthepresenceoisnacidic p lymerisation catalyst and on aliphaticether andrecoverinaprecipitatedmetaldehycbfromthereactionmixturebyiiltration.

3. A process for prepcrin: metsidchyde which comprises acetaldehwdebelow ani50.inthepreseneeotanaliphetic other containing not more than 8carbon atoms.

4. A process for preparing metaidehyde which comprises polymerizingacetaldehyde below anproximstelyifi'ainthepresenceoi'anacidicpolymerisation catalyst and an aliphatic ether.

containinsnotmorethantcarbonatoms.and.

recovering precipitated in from the reaction mixture by nitration.

5. A process for preparing metaldehyde which comprises polymerisinoacetaidehyde below anproxirnstely 15' C. in the presence 0! di-ethyl 8.A process for preparinl mstsldehirde which comprises polymerizingaeeialdehyde below ep- 150.inthepsesenceotanacidic pclymerilltioncatalyst and di-ethyl ether and recovering precipitated metaldehyde fromthe reactionmixtuiehyflltration.

7. A process for prepsrinl metaldehyde which pobmerlsihi scetaldehydebelow approximately 15' O. inthe presence or di-isomcwi W rewverln: m bytitration rromthe reactionmixture.

I. A process for preperins meteldehyde which comprises polymerizingaoetaldehyde below an proximately 15' C. in the presence of dioxane andthereafter recovering metaldehyde y filtration from the reactionmixture.

9. A process for preparing metaldehyde which 5 tiaily pure precipitatedmetaldehyde from the re- 16 action mixture by filtration.

RICHARD 8. WILDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNrrmS STATES PATENTS Number Name Date 2,318,341 Thompson May 4, 19432,327,570 Vogel Aug. 20, 1943 1,300,451 Morton et a1 Apr. 15, 1919 OTHERREFERENCES Merck Index, 5th edition, pages 352 and 413.

